Some addition to the generalized Riemann-Hilbert problem

We give some additions to the article "On the generalized Riemann-Hilbert problem with irregular singularities" by Bolibruch, Malek, Mitschi (math/0410483). In particular, a weak GRH-problem and the GRH-problem for scalar differential equations are discussed.Comment: 19 pages, an extended version of the article submitted to Ann. Fac. Sci. Toulous